Alfalfa Roots Research Articles

Exploring the influence of alfalfa root reinforcement on the loess slopes reliability analysis

Exploring the influence of alfalfa root reinforcement on the loess slopes reliability analysis

The overlooked salt: Impact of dark septate endophytes on alfalfa at varying sodium sulfate levels

Sodium sulfate (Na2SO4) is one sodium salt extensively found in saline soils; in certain regions, it is the dominant salt present. Dark septate endophytes (DSE) are competent in enhancing plants’ resistance to stressed environments. Nevertheless, little is known about the role of DSE in enhancing plant tolerance to Na2SO4. This study examined DSE growth and its impacts on alfalfa plants exposed to varying Na2SO4 concentrations (0%, 0.15%, 0.3%, and 0.45% (w/w)). Our findings revealed that DSE can thrive even in salt-stress environments. On the 8th day of cultivation, their biomass reached the highest level under 0.45% salt concentration. Moreover, DSE successfully colonized alfalfa roots and significantly enhanced plant growth and development across the various salt gradients. Notably, DSE made the highest contribution 68% to the total biomass of alfalfa at 0.45% salt concentration. Meanwhile, DSE significantly decreased the presence of root’s Na+ across varying salt gradients. Additionally, DSE significantly increased catalase (CAT) activity at salt concentrations of 0.3% and 0.45%. Our study also revealed strong positive correlations of plant biomass with the root index, root’s K+ content, and K+/Na+ ratio, and strong negative correlations of plant biomass with root’s Na+ content and soil’s Na+ and SO42− contents. Structural equation modeling (SEM) demonstrated that DSE indirectly enhanced plant’s shoot biomass under various salt stresses via increasing root length, decreasing root’s Na+ content, and raising CAT activity, while salt indirectly reduced plant’s shoot weight via reducing root length or increasing root’s Na+ content or exerted a direct negative effect on plant shoot biomass. Thus, DSE are instrumental in bolstering the salt tolerance of plants, which holds strategic importance for the management of saline-alkali soils.

Comparative transcriptome analysis to identify the important mRNA and lncRNA associated with salinity tolerance in alfalfa.

Salinity represents a fatal factor affecting the productivity of alfalfa. But the regulation of salinity tolerance via lncRNAs and mRNAs remains largely unclear within alfalfa. For evaluating salinity stress resistance-related lncRNAs and mRNAs within alfalfa, we analyzed root transcriptomics in two alfalfa varieties, GN5 (salinity-tolerant) and GN3 (salinity-sensitive), after treatments with NaCl at 0 and 150 mM. There were altogether 117,677 lncRNAs and 172,986 mRNAs detected, including 1,466 lncRNAs and 2,288 mRNAs with significant differential expression in GN5150/GN50, GN3150/GN30, GN50/GN30, and GN5150/GN3150. As revealed by GO as well as KEGG enrichment, some ionic and osmotic stress-associated genes, such as HPCA1-LRR, PP2C60, PP2C71, CRK1, APX3, HXK2, BAG6, and ARF1, had up-regulated levels in GN5 compared with in GN3. In addition, NaCl treatment markedly decreased CNGC1 expression in GN5. According to co-expressed network analyses, six lncRNAs (TCONS_00113549, TCONS_00399794, TCONS_00297228, TCONS_00004647, TCONS_00033214 and TCONS_00285177) modulated 66 genes including ARF1, BAG6, PP2C71, and CNGC1 in alfalfa roots, suggesting that these nine genes and six lncRNAs probably facilitated the different salinity resistance in GN5 vs. GN3. These results shed more lights on molecular mechanisms underlying genotype difference in salinity tolerance among alfalfas.

Riparian restoration in sandy zones with alfalfa as pioneer plant in initial stage of soil and water bioengineering

As Nature-Based and Bio-based Solutions, soil and water bioengineering (SWB) provides several benefits to humans and nature. It has been widely used for erosion control, vegetation recovery and ecosystem restoration in riparian zones. Nevertheless, studies on riparian restoration in sandy zones with alfalfa as pioneer plant in initial stage of SWB are still rare, which are important for understanding the role of pioneer plants during the initial stage of SWB and also for choice of the appropriate measures. Here, three commonly applied SWB measures (vegetation geobag / VGB, grass-planting concrete block / GCB, and untreated flat area / NTF) are established in sandy riparian zones to explore the growth characteristics structural mechanics and reinforcement of pioneer plant (alfalfa) root, and also the factors influencing biomechanical properties in initial stage of SBE. Our results show that: (1)NTF demonstrated superior overall growth compared to GCB and VGB, underscoring the limitations that geobags and steep slopes impose on initial SWB vegetation establishment. In all treatments, alfalfa roots were able to penetrate soil layers below 60 cm, with NTF exhibiting the highest root biomass and diameter (NTF > GCB > VGB). GCB's higher root-to-shoot ratio may reflect a drought-resistant strategy. In contrast, VGB showed greater root length, maximum rooting depth, and a smaller crown width, indicating a focus on root growth to overcome geobag constraints (2) Differences in root growth distribution among the three treatments resulted in varying biomechanical impacts. Specifically, NTF exhibited significantly lower soil-root bond strength than GCB, while both NTF and GCB had higher maximum pull-out forces compared to VGB. Root diameter showed a significant negative correlation with Young's modulus and root tensile strength, but a positive correlation with root tensile force (p < 0.05). Although no significant correlations were found between root water content and root tensile strength, root tensile strength was positively correlated with Young's modulus. (3) In the comprehensive evaluation of root reinforcement performance, the scores ranked as VGB > GCB > NTF. Result of this study could provide valuable insights into the practical applications of SWB in sandy riparian restoration. Furthermore, it underscores the importance of pioneer plants in the fragile and critical initial stages of SWB, and also benefit both researchers and practitioners in effectively transitioning from the scientific research to practical solutions for riparian restoration.

Infection Process of Alfalfa Root Rot Caused by Fusarium acuminatum

Fusarium spp. can cause root rot in alfalfa, leading to the death of the whole plant, which seriously affects the yield and quality of alfalfa. This study used a Fusarium acuminatum strain labeled with green fluorescent protein (GFP) to observe the infection process of F. acuminatum on alfalfa by confocal fluorescence microscopy. The aim of this study was to reveal the infection mechanism of alfalfa Fusarium root rot at the cellular histological level. The results showed that conidia of F. acuminatum attached to the surface of the root and germinated at one day post-inoculation, the mycelium then entered the vascular bundle tissue of the alfalfa root at 5 days post-inoculation, reached the base of the plant stem at 14 days post-inoculation, and colonized the stem of the first and second compound leaf at 28 and 49 days post-inoculation, respectively. Moreover, the experiment, which sprayed a spore suspension, showed that the conidia of F. acuminatum could spread through the air to infect the pericarp and seed coat tissue of the pod. For the first time, we report the infection process of alfalfa Fusarium root rot caused by F. acuminatum and clarify that F. acuminatum can initially infect the root tissue of alfalfa, colonize the bottom stem of the plant through systematic infection, and eventually cause the plant to wilt and die. The results reveal the infection mechanism of F. acuminatum at the cell level via histology and provide theoretical support for the development of control strategies and key control technologies for alfalfa root rot.

Biological Decline of Alfalfa Is Accompanied by Negative Succession of Rhizosphere Soil Microbial Communities.

The growth and biological decline of alfalfa may be linked to the rhizosphere microbiome. However, plant-microbe interactions in the rhizosphere of alfalfa and associated microbial community variations with stand age remain elusive. This study explored the successional pattern of rhizosphere microbial communities across different aged alfalfa stands and its relationship with alfalfa decline. Rhizosphere soils were collected from 2- and 6-year-old alfalfa stands. Control soils were collected from interspaces between alfalfa plants in the same stands. Soil bacterial and fungal communities were characterized by 16S and ITS rRNA gene sequencing, respectively. Specific microbial taxa colonized the rhizosphere soils, but not the control soils. The rhizosphere-specific taxa mainly included potentially beneficial genera (e.g., Dechloromonas, Verrucomicrobium) in the young stand and harmful genera (e.g., Peziza, Campylocarpon) in the old stand. Alfalfa roots regulated soil microbial communities by selective promotion or inhibition of distinct taxa. The majority of time-enriched taxa were reported as harmful fungi, whose relative abundances were negatively correlated with plant traits. Time-depleted taxa were mostly known as beneficial bacteria, which had relative abundances positively correlated with plant traits. The relative abundances of functional bacterial genes associated with vancomycin biosynthesis, zeatin biosynthesis, and amino acid metabolism trended lower in rhizosphere soils from the old stand. An upward trend was observed for fungal pathogens and wood saprotrophs with increasing stand age. The results suggest that root activity drives the negative succession of rhizosphere microbial communities during alfalfa decline in old stands.

Thriving in a salty future: morpho-anatomical, physiological, and molecular adaptations to salt stress in alfalfa (Medicago sativa L.) and other crops.

With soil salinity levels rising at an alarming rate, accelerated by climate change and human interventions, there is a growing need for crop varieties that can grow on saline soils. Alfalfa (Medicago sativa) is a cool-season perennial leguminous crop, commonly grown as forage, biofuel feedstock, and soil conditioner. It demonstrates significant potential for agricultural circularity and sustainability, for example by fixing nitrogen, sequestering carbon, and improving soil structures. Although alfalfa is traditionally regarded as moderately salt-tolerant species, modern alfalfa varieties display specific salt-tolerance mechanisms, which could be used to pave alfalfa's role as a leading crop able to grow on saline soils. Alfalfa's salt tolerance underlies a large variety of cascading biochemical and physiological mechanisms. These are partly enabled by alfalfa's complex genome structure and out-crossing nature, which on the other hand entail impediments for molecular and genetic studies. This review first summarizes the general effects of salinity on plants and the broad-ranging mechanisms for dealing with salt-induced osmotic stress, ion toxicity, and secondary stress. Secondly, we address defensive and adaptive strategies that have been described for alfalfa, such as the plasticity of alfalfa's root system, hormonal crosstalk for maintaining ion homeostasis, spatiotemporal specialized metabolite profiles, and the protection of alfalfa-rhizobia associations. Finally, bottlenecks for research of the physiological and molecular salt-stress responses as well as biotechnology-driven improvements of salt tolerance are identified and discussed. Understanding morpho-anatomical, physiological, and molecular responses to salinity is essential for the improvement of alfalfa and other crops in saline land reclamation. This review identifies potential breeding targets for enhancing alfalfa performance stability and general crop robustness for rising salt levels as well as to promote alfalfa applications in saline land management.

Phenotyping Alfalfa (Medicago sativa L.) Root Structure Architecture via Integrating Confident Machine Learning with ResNet-18.

Background: Root system architecture (RSA) is of growing interest in implementing plant improvements with belowground root traits. Modern computing technology applied to images offers new pathways forward to plant trait improvements and selection through RSA analysis (using images to discern/classify root types and traits). However, a major stumbling block to image-based RSA phenotyping is image label noise, which reduces the accuracies of models that take images as direct inputs. To address the label noise problem, this study utilized an artificial intelligence model capable of classifying the RSA of alfalfa (Medicago sativa L.) directly from images and coupled it with downstream label improvement methods. Images were compared with different model outputs with manual root classifications, and confident machine learning (CL) and reactive machine learning (RL) methods were tested to minimize the effects of subjective labeling to improve labeling and prediction accuracies. Results: The CL algorithm modestly improved the Random Forest model's overall prediction accuracy of the Minnesota dataset (1%) while larger gains in accuracy were observed with the ResNet-18 model results. The ResNet-18 cross-population prediction accuracy was improved (~8% to 13%) with CL compared to the original/preprocessed datasets. Training and testing data combinations with the highest accuracies (86%) resulted from the CL- and/or RL-corrected datasets for predicting taproot RSAs. Similarly, the highest accuracies achieved for the intermediate RSA class resulted from corrected data combinations. The highest overall accuracy (~75%) using the ResNet-18 model involved CL on a pooled dataset containing images from both sample locations. Conclusions: ResNet-18 DNN prediction accuracies of alfalfa RSA image labels are increased when CL and RL are employed. By increasing the dataset to reduce overfitting while concurrently finding and correcting image label errors, it is demonstrated here that accuracy increases by as much as ~11% to 13% can be achieved with semi-automated, computer-assisted preprocessing and data cleaning (CL/RL).

Complete genomes of two Variovorax endophytes isolated from surface-sterilized alfalfa nodules.

Variovorax species catabolize a wide range of natural and industrial products and have been shown to be integral rhizosphere inhabitants. Here, we report the complete genomes of V. paradoxus 2u118 and V. sp. SPNA7, which were isolated from alfalfa root nodules and possess plant growth-promoting properties.

Comparative proteomic discovery of salt stress response in alfalfa roots and overexpression of MsANN2 confers salt tolerance

Soil salinity constrains growth, development and yield of alfalfa (Medicago sativa L.). To illustrate the molecular mechanisms responsible for salt tolerance, a comparative proteome analysis was explored to characterize protein profiles of alfalfa seedling roots exposed to 100 and 200 mM NaCl for three weeks. There were 52 differentially expressed proteins identified, among which the mRNA expressions of 12 were verified by Real-Time-PCR analysis. The results showed increase in abundance of ascorbate peroxidase, POD, CBS protein and PR-10 in salt-stressed alfalfa, suggesting an effectively antioxidant and defense systems. Alfalfa enhanced protein quality control system to refold or degrade abnormal proteins induced by salt stress through upregulation of unfolded protein response (UPR) marker PDIs and molecular chaperones (eg. HSP70, TCP-1, and GroES) as well as the ubiquitin‐proteasome system (UPS) including ubiquitin ligase enzyme (E3) and proteasome subunits. Upregulation of proteins responsible for calcium signal transduction including calmodulin and annexin helped alfalfa adapt to salt stress. Specifically, annexin (MsANN2), a key Ca2+-binding protein, was selected for further characterization. The heterologous of the MsANN2 in Arabidopsis conferred salt tolerance. These results provide detailed information for salt-responsive root proteins and highlight the importance of MsANN2 in adapting to salt stress in alfalfa.

Study the effect of Enterobacter cloacae on the gene expression, productivity, and quality traits of Curcuma longa L. Plant.

Overuse of artificial chemical fertilizers could be detrimental to the environment. Utilizing beneficial microorganisms as biofertilizers is a sustainable technique that promotes soil health, crop yield, and ecosystem preservation. Curcuma longa L. is utilized as a medication since it has its antibacterial, anti-microbial, and anti-tumor characteristics, which reduce inflammation and hasten wound healing. The effect of E. cloacae strain MSR1, which is common in the roots of alfalfa grown in the Al-Ahsaa region, on C. longa plants is being investigated. C. longa rhizomes were planted under greenhouse conditions after being submerged in a solution of E. cloacae strain MSR1 (OD 500) or water treatment as a control for 12 hours. After 240 days of growing, ten randomly selected plants from each treatment were collected, and the vegetative growth and yield metrics were assessed. To investigate how E. cloacae influences C. longa production and chemical composition (photosynthetic pigment, nitrogen, phosphorus, potassium, and curcuminoid), measurements were conducted as well as genes diketide-CoA and curcumin synthases genes. Our research showed that C. longa's growth and yield were favorably impacted by E. cloacae. Significant increases in the related plants' chlorophyll a,b, carotenoid, nitrogen, phosphorus, and potassium levels were likewise a reflection of the enhanced effects shown in the growth and yield parameters. Treatment with E. cloacae raised the curcuminoid's three sub-components' compositions to varying degrees: bisdemethoxycurcumin, demethoxycurcumin, and curcumin. Comparing E. cloacae treated plants to the control, high expression levels of the genes diketide-CoA and curcumin synthase-1, -2, and 3 were also found. The treatment of E. cloacae is a good biostimulant candidate for boosting growth and yield as well as raising the medicinal qualities of C. longa, according to the overall results.

Genomics and taxonomy of the glyphosate-degrading, copper-tolerant rhizospheric bacterium Achromobacter insolitus LCu2.

A rhizosphere strain, Achromobacter insolitus LCu2, was isolated from alfalfa (Medicago sativa L.) roots. It was able to degrade of 50% glyphosate as the sole phosphorus source, and was found resistant to 10mM copper (II) chloride, and 5mM glyphosate-copper complexes. Inoculation of alfalfa seedlings and potato microplants with strain LCu2 promoted plant growth by 30-50%. In inoculated plants, the toxicity of the glyphosate-copper complexes to alfalfa seedlings was decreased, as compared with the noninoculated controls. The genome of A. insolitus LCu2 consisted of one circular chromosome (6,428,890bp) and encoded 5843 protein genes and 76 RNA genes. Polyphasic taxonomic analysis showed that A. insolitus LCu2 was closely related to A. insolitus DSM23807T on the basis of the average nucleotide identity of the genomes of 22 type strains and the multilocus sequence analysis. Genome analysis revealed genes putatively responsible for (1) plant growth promotion (osmolyte, siderophore, and 1-aminocyclopropane-1-carboxylate deaminase biosynthesis and auxin metabolism); (2) degradation of organophosphonates (glyphosate oxidoreductase and multiple phn clusters responsible for the transport, regulation and C-P lyase cleavage of phosphonates); and (3) tolerance to copper and other heavy metals, effected by the CopAB-CueO system, responsible for the oxidation of copper (I) in the periplasm, and by the efflux Cus system. The putative catabolic pathways involved in the breakdown of phosphonates are predicted. A. insolitus LCu2 is promising in the production of crops and the remediation of soils contaminated with organophosphonates and heavy metals.

Root-Zone Bacterial Diversity in Field-Grown Individual Plants from Alfalfa Lines with Wild Relatives in Their Genetic Backgrounds

Alfalfa (Medicago sativa L.) is a vitally important perennial fodder legume worldwide. Given their particular traits, alfalfa crop wild relatives (CWRs) could be used to develop cultivars that can tolerate extreme environmental and climatic conditions. Until now, researchers have overlooked the composition and structure of bacterial communities in the root zone of alfalfa and its relevant CWRs and their influence on forage performance under actual field conditions. In this study, high-throughput sequencing of 16S rRNA analysis was performed to investigate the diversity and assemblies of bacterial communities in the bulk soil and in the root zone of individual field-grown Medicago plants arranged in a honeycomb selection design. The plants used in this study were M. sativa × M. arborea hybrids (Genotypes 6 and 8), the closely-related M. sativa nothosubsp. varia (Martyn) Arcang. (Genotype 13), and M. sativa ssp. sativa (Genotype 20). The bacterial communities in the root-zone samples and the assemblies in the bulk soil differed significantly. Genotype 13 was found to have distinct bacterial assemblies from the other genotypes while exhibiting the lowest forage productivity. These findings suggest that plant productivity may influence the composition of bacterial communities in the root zone. Biomarker analysis conducted using linear discriminant analysis (LDA) revealed that only members of the Rhizobiales order were enriched in the M. sativa nothosubsp. varia root zone whereas taxa belonging to Sphingomonas and various Bacteriodota were enriched in the other genotypes. Of the shared taxa identified in the root zone of the Medicago lines, the abundance of specific taxa, namely, Flavisolibacter, Stenotrophomonas, and Sphingomonas, were positively associated with forage yield. This pioneering study, in which the root zones of individual Medicago plants under actual field conditions were examined, offers evidence of differences in the bacterial composition of alfalfa genotypes with varying genetic backgrounds. Its findings indicate that particular bacterial taxa may favorably influence plant performance. This study covered the first six months of crop establishment and paves the way for further investigations to advance understanding of how shifts in bacterial assemblies in alfalfa roots affect plant performance over time.

Ferric Oxide Nanomaterials and Plant-Rhizobacteria Symbionts Cogenerate Iron Plaque for Removing Highly Chlorinated Contaminants in Dryland Soils.

Rhizosphere iron plaques derived from Fe-based nanomaterials (NMs) are a promising tool for sustainable agriculture. However, the requirement for flooded conditions to generate iron plaque limits the scope of the NM application. In this study, we achieved in situ Fenton oxidation of a highly chlorinated persistent organic pollutant (2,2',4,5,5'-pentachlorobiphenyl, PCB101) through iron plaque mediated by the interaction between α-Fe2O3 NMs and plant-rhizobacteria symbionts under dryland conditions. Mechanistically, the coexistence of α-Fe2O3 NMs and Pseudomonas chlororaphis JD37 stimulated alfalfa roots to secrete acidic and reductive agents as well as H2O2, which together mediated the rhizosphere Fenton reaction and converted α-Fe2O3 NMs into iron plaque rich in Fe(II)-silicate. Further verifications reproduced the Fenton reaction in vitro using α-Fe2O3 NMs and rhizosphere compounds, confirming the critical role of •OH in the oxidative degradation of PCB101. Significant reductions in PCB101 content by 18.6%, 42.9%, and 23.2% were respectively found in stem, leaf, and soil after a 120-d treatment, proving the effectiveness of this NMs-plant-rhizobacteria technique for simultaneously safe crop production and soil remediation. These findings can help expand the potential applications of nanobio interaction and its mediated iron plaque generation for both agricultural practice and soil remediation.

Alfalfa Spring Black Stem and Leaf Spot Disease Caused by Phoma medicaginis: Epidemic Occurrence and Impacts.

Alfalfa spring black stem and leaf spot disease (ASBS) is a cosmopolitan soil-borne and seed-borne disease caused by Phoma medicaginis, which adversely affects the yield, and nutritive value and can stimulate production of phyto-oestrogenic compounds at levels that may adversely affect ovulation rates in animals. This review summarizes the host range, damage, and symptoms of this disease, and general features of the infection cycle, epidemic occurrence, and disease management. ASBS has been reported from over 40 countries, and often causes severe yield loss. Under greenhouse conditions, reported yield loss was 31-82% for roots, 32-80% for leaves, 21% for stems and 26-28% for seedlings. In field conditions, the forage yield loss is up to 56%, indicating that a single-cut yield of 5302 kg/ha would be reduced to 2347 kg/ha. P. medicaginis can infect up to 50 species of plants, including the genera Medicago, Trifolium, Melilotus, and Vicia. ASBS is more severe during warm spring conditions before the first harvest than in hot summer and cooler winter conditions, and can infect alfalfa roots, stems, leaves, flowers, pods, and seeds, with leaf spot and/or black stem being the most typical symptoms. The primary infection is caused by the overwintering spores and mycelia in the soil, and on seeds and the cortex of dead and dry stems. The use of resistant cultivars is the most economical and effective strategy for the control of ASBS. Although biological control has been studied in the glasshouse and is promising, chemical control is the main control method in agriculture.

Phosphorus uptake and rhizosphere properties of alfalfa in response to phosphorus fertilizer types in sandy soil and saline-alkali soil.

Phosphorus (P) fertilizer is critical to maintain a high yield and quality of alfalfa (Medicago sativa L.). There are several fertilizer types and soil types in China, and the application of a single type of P fertilizer may not be suitable for present-day alfalfa production. In order to select the optimal combination of alfalfa and soil type and fertilizer type for improving P utilization efficiency. We conducted a greenhouse pot experiment, calcium superphosphate (SSP), diammonium phosphate (DAP), ammonium polyphosphate (APP), potassium dihydrogen phosphate (KP), and no-fertilizer control treatments were applied to alfalfa in sandy and saline-alkali soils. The response of alfalfa root morphology and rhizosphere processes to different P fertilizers was investigated. The results showed that shoot biomass of alfalfa was slightly higher in sandy soil than in saline-alkali soil. Shoot biomass of alfalfa increased by 223%-354% in sandy soil under P treatments compared with the control, and total root length increased significantly by 74% and 53% in DAP and SSP treatments, respectively. In saline-alkali soil, alfalfa shoot biomass was significantly increased by 229% and 275% in KP and DAP treatments, and total root length was increased by 109% only in DAP treatment. Net P uptake of alfalfa in DAP treatment was the highest in both soils, which were 0.73 and 0.54 mg plant-1, respectively. Alfalfa shoot P concentration was significantly positively correlated with shoot and root biomass (P < 0.05, 0.01 or 0.001) whereas negatively correlated with acid phosphatase concentration (P < 0.05). Improvement of plant growth and P uptake induced by P fertilizer application was greater in sandy soil than in saline-alkali soil. DAP and KP was the most efficient P fertilizers in both sandy soil and saline-alkali soil.

Degradation of petroleum hydrocarbon contaminants by Rhodococcus erythropolis KB1 synergistic with alfalfa (Medicago sativa L.).

Petroleum hydrocarbons are a stubborn pollutant that is difficult to degrade globally, and plant-microbial degradation is the main way to solve this type of pollutant. In this study, the physiological and ecological responses of alfalfa to petroleum hydrocarbons in different concentrations of petroleum hydrocarbon-contaminated soil with KB1 (Rhodococcus erythropolis) were analyzed and determined by laboratory potting techniques. The growth of alfalfa (CK) and alfalfa with KB1 (JZ) in different concentrations of petroleum hydrocarbons contaminated soil was compared and analyzed. The results of the CK group showed that petroleum hydrocarbons could significantly affect the activity of alfalfa antioxidant enzyme system, inhibit the development of alfalfa roots and the normal growth of plants, especially in the high-concentration group. KB1 strain had the ability to produce IAA, form biofilm, fix nitrogen, produce betaine and ACC deaminase, and the addition of KB1 could improve the growth traits of alfalfa in the soil contaminated with different concentrations of petroleum hydrocarbons, the content of soluble sugars in roots, and the stress resistance and antioxidant enzyme activities of alfalfa. In addition, the degradation kinetics of the strain showed that the degradation rate of petroleum could reach 75.2% after soaking with KB1. Furthermore, KB1 can efficiently degrade petroleum hydrocarbons in advance and significantly alleviate the damage of high concentration of petroleum hydrocarbons to plant roots. The results showed that KB1 strains and alfalfa plants could effectively enhance the degradation of petroleum hydrocarbons, which provided new ideas for improving bioremediation strategies.

Transcriptomic analysis provides insights into the molecular mechanism of melatonin-mediated cadmium tolerance in Medicago sativa L.

Cadmium (Cd), a toxic element, often makes a serious threat to plant growth and development. Previous studies found that melatonin (Mel) reduced Cd accumulation and reestablished the redox balance to alleviate Cd stress in Medicago sativa L., however, the complex molecular mechanisms are still elusive. Here, comparative transcriptome analysis and biochemical experiments were conducted to explore the molecular mechanisms of Mel in enhancing Cd tolerance. Results showed that 7237 differentially expressed genes (DEGs) were regulated by Mel pretreatment to Cd stress compared to the control condition in roots of Medicago sativa L. Besides, in comparison with Cd stress alone, Mel upregulated 1081 DEGs, and downregulated 1085 DEGs. These DEGs were mainly involved in the transcription and translation of genes and folding, sorting and degradation of proteins, carbohydrate metabolism, and hormone signal network. Application of Mel regulated the expression of several genes encoding ribosomal protein and E3 ubiquitin-protein ligase involved in folding, sorting and degradation of proteins. Moreover, transcriptomic analyse suggested that Mel might regulate the expression of genes encoding pectin lyase, UDP-glucose dehydrogenase, sucrose-phosphate synthase, hexokinase-1, and protein phosphorylation in the sugar metabolism. Therefore, these could promote sucrose accumulation and subsequently alleviate the Cd damage. In conclusion, above findings provided the mining of important genes and molecular basis of Mel in mitigating Cd tolerance and genetic cultivation of Medicago sativa L.

The trade-off regulation of arbuscular mycorrhiza on alfalfa growth dose-dependent on gradient Mo exposure

Molybdenum (Mo) is an essential nutrient for leguminous plants, but the effects of Mo exposure on plant growth, especially in relation to soil microorganisms, are not fully understood. This study employed alfalfa (Medicago sativa L.) to evaluate the physiochemical responses to gradient soil Mo variations and explore the potential regulatory role of rhizosphere microorganism - arbuscular mycorrhizal fungi (AMF) in modulating Mo's impact on plant physiology, with a focus on metabolic pathways. The results showed that Mo exerted hormetic effect (facilitation at low doses; inhibition at high doses) on alfalfa growth, promoting biomass (below 90.94 mg/kg, with a 63.98 % maximum increase), root length (below 657.11 mg/kg, with a 39.29 % maximum increase), and plant height (below 304.03 mg/kg, with an 18.4 % maximum increase). Excess Mo (1000 mg/kg) resulted in a reduction in photosynthesis and biomass growth due to increased oxidative stress (p < 0.05). Within the stimulatory zones, AMF enhanced Mo accumulation in alfalfa, augmenting its phytological effects. Exceed the stimulatory zones, AMF enhanced alfalfa Fe uptake and reduced the generation of reactive oxygen species (ROS) induced by excess Mo by shifting the redox homeostasis-controlled enzyme from peroxidase (POD) to superoxide dismutase (SOD), thereby improving alfalfa's tolerance to Mo. Metabolomic analysis further revealed that AMF promoted the biosynthesis of indole acetic acid (IAA) and various amino acids in Mo-stressed alfalfa (p < 0.05), which accelerated alfalfa growth and mitigated Mo-induced phytotoxicity. These insights provide a foundation for developing sustainable management strategies for Mo-exposed soils using AMF inoculants, such as minimizing Mo fertilizer application in Mo-deficient soils and facilitating the reclamation of Mo-contaminated soils.

Isolation and characterization of rhizobia and evaluation of their effect on radish (Raphanus Sativus ) growth

This study focused on isolating and characterizing rhizobia from alfalfa root nodules and assessing their impact on Radish (Raphanus sativus L) growth. Fifteen isolates underwent morphological and biochemical analyses, revealing consistent traits with variations in colony elevation. Confirmatory tests identified all isolates as gram-negative, rod-shaped, catalase, and oxidase positive. Notably, 13 isolates exhibited citrate positivity, 14 urease positivity, and 2 gelatinase positivity. Ten isolates produced indole-3-acetic acid, nine solubilized phosphate, and all produced ammonia. R12 displayed the highest seed germination (100%). Significant effects (P &lt; 0.05) on radish growth were observed, with R37 yielding the highest values for root length (19 cm), R5 for shoot length (9 cm), R5 for leaf number (12.6), R36 for fresh weight (8 g), and R37 for dry weight (5 g). These superior isolates hold potential as biofertilizers for enhancing radish growth. Bangladesh J. Bot. 53(1): 185-192, 2024 (March)